1. Field of the Invention
The invention relates generally to the field of photography, and in particular to a film cassette containing a film roll. More specifically, the invention relates to a film cassette capable of advancing a film leader from inside the cassette shell to outside the cassette shell responsive to unwinding rotation of a spool supporting the film roll.
2. Description of the Prior Art
Commonly assigned U.S. Pat. No. 4,832,275, issued May 23, 1989 discloses a film cassette wherein a spool core is supported inside a cassette shell for rotation in an unwinding direction about an axis, a film roll coiled about the spool core is advanced beginning with a leading film end at an outermost convolution of the film roll from inside the cassette shell to outside the cassette shell in response to rotation of the spool core in the unwinding direction, and a pair of rigid constraining rings are supported for rotation about separate axes each inclined with respect to the axis of the spool core to position the constraining rings partially encircling the outermost film convolution to radially confine the outermost film convolution in order to prevent it from clockspringing against an interior curved wall of the cassette shell and to position the constraining rings partially not encircling the outermost film convolution to allow the outermost film convolution beginning with the leading film end to escape radial confinement of the constraining rings when the spool core is rotated in the unwinding direction.